The phenomenon where measuring signal goes in overload is cause by the high impedance of an amplifier. Whenever the input impedance is higher than for example 10 MOhm that channel will go into overload. For example: for STG amplifiers in 10V range where the input impedance is higher than 1 GOhm even the smallest input changes such as voltage, temperature, noise,... can cause the signal to go into overload.A quick test to check this is:
In channel setup set the measuring range to 0.1 V and click on the "Short On" button:

All channels will go to 0,0000V or whatever the specified error of each module is.